winston

A multi-transport async logging library for node.js. "CHILL WINSTON! ... I put it in the logs."

Installation

Installing npm (node package manager)

curl http://npmjs.org/install.sh | sh

Installing winston

[sudo] npm install winston

Motivation

Winston is designed to be a simple and universal logging library with support for multiple transports. A transport is essentially a storage device for your logs. Each instance of a winston logger can have multiple transports configured at different levels. For example, one may want error logs to be stored in a persistent remote location (like a database), but all logs output to the console or a local file.

There also seemed to be a lot of logging libraries out there that coupled their implementation of logging (i.e. how the logs are stored / indexed) to the API that they exposed to the programmer. This library aims to decouple those parts of the process to make it more flexible and extensible.

Usage

There are two different ways to use winston: directly via the default logger, or by instantiating your own Logger. The former is merely intended to be a convenient shared logger to use throughout your application if you so choose.

Using the Default Logger

The default logger is accessible through the winston module directly. Any method that you could call on an instance of a logger is available on the default logger:

Handling Uncaught Exceptions with winston

With winston, it is possible to catch and log uncaughtException events from your process. There are two distinct ways of enabling this functionality either through the default winston logger or your own logger instance.

If you want to use this feature with the default logger simply call .handleExceptions() with a transport instance.

//// You can add a separate exception logger by passing it to `.handleExceptions`//
winston.handleExceptions(newwinston.transports.File({ filename:'path/to/exceptions.log' }))
//// Alternatively you can set `.handleExceptions` to true when adding transports to winston//
winston.add(winston.transports.File, {
filename:'path/to/all-logs.log',
handleExceptions:true
});
winston.handleExceptions();

When working with custom logger instances, you can pass in separate transports to the exceptionHandlers property or set .handleExceptions on any transport.

Using Logging Levels

Setting the level for your logging message can be accomplished in one of two ways. You can pass a string representing the logging level to the log() method or use the level specified methods defined on every winston Logger.

//// Any logger instance//
logger.log('info', "127.0.0.1 - there's no place like home");
logger.info("127.0.0.1 - there's no place like home");
//// Default logger//
winston.log('info', "127.0.0.1 - there's no place like home");
winston.info("127.0.0.1 - there's no place like home");

//// Change levels on the default winston logger//
winston.setLevels(winston.config.syslog.levels);
//// Change levels on an instance of a logger//
logger.setLevels(winston.config.syslog.levels);

Calling .setLevels on a logger will remove all of the previous helper methods for the old levels and define helper methods for the new levels. Thus, you should be careful about the logging statements you use when changing levels. For example, if you ran this code after changing to the syslog levels:

//// Logger does not have 'silly' defined since that level is not in the syslog levels //
logger.silly('some silly message');

Using Custom Logging Levels

In addition to the predefined npm and syslog levels available in Winston, you can also choose to define your own:

Although there is slight repetition in this data structure, it enables simple encapsulation if you not to have colors. If you do wish to have colors, in addition to passing the levels to the Logger itself, you must make winston aware of them:

//// Make winston aware of these colors//
winston.addColors(myCustomLevels.colors);

This enables transports with the 'colorize' option set to appropriately color the output of custom levels.

Events and Callbacks in Winston

Each instance of winston.Logger is also an instance of an EventEmitter. A log event will be raised each time a transport successfully logs a message:

Working with multiple Loggers in winston

Often in larger, more complex applications it is necessary to have multiple logger instances with different settings. Each logger is responsible for a different feature area (or category). This is exposed in winston in two ways: through winston.loggers and instances of winston.Container. In fact, winston.loggers is just a predefined instance of winston.Container:

All profile messages are set to the 'info' by default and both message and metadata are optional There are no plans in the Roadmap to make this configurable, but I'm open to suggestions / issues.

Using winston in a CLI tool

A common use-case for logging is output to a CLI tool. Winston has a special helper method which will pretty print output from your CLI tool. Here's an example from the require-analyzer written by Nodejitsu:

Extending another object with Logging functionality

Often in a given code base with lots of Loggers it is useful to add logging methods a different object so that these methods can be called with less syntax. Winston exposes this functionality via the 'extend' method:

var myObject = {};
logger.extend(myObject);
//// You can now call logger methods on 'myObject'//
myObject.info('127.0.0.1 - there's no place like home');

Working with Transports

Right now there are four transports supported by winston core. If you have a transport you would like to add either open an issue or fork and submit a pull request. Commits are welcome, but I'll give you extra street cred if you add tests too :D

Console: Output to the terminal

Files: Append to a file

Loggly: Log to Logging-as-a-Service platform Loggly

Console Transport

winston.add(winston.transports.Console, options)

The Console transport takes two simple options:

level: Level of messages that this transport should log.

silent: Boolean flag indicating whether to suppress output

colorize: Boolean flag indicating if we should colorize output.

Metadata: Logged via util.inspect(meta);

File Transport

winston.add(winston.transports.File, options)

The File transport should really be the 'Stream' transport since it will accept any WritableStream. It is named such because it will also accept filenames via the 'filename' option:

level: Level of messages that this transport should log.

silent: Boolean flag indicating whether to suppress output.

colorize: Boolean flag indicating if we should colorize output.

filename: The filename of the logfile to write output to.

stream: The WriteableStream to write output to.

Metadata: Logged via util.inspect(meta);

Loggly Transport

winston.add(winston.transports.Loggly, options);

The Loggly transport is based on Nodejitsu'snode-loggly implementation of the Loggly API. If you haven't heard of Loggly before, you should probably read their value proposition. The Loggly transport takes the following options. Either 'inputToken' or 'inputName' is required:

collection: The name of the collection you want to store log messages in, defaults to 'log'.

safe: Boolean indicating if you want eventual consistency on your log messages, if set to true it requires an extra round trip to the server to ensure the write was committed, defaults to true.

host: The host running MongoDB, defaults to localhost.

port: The port on the host that MongoDB is running on, defaults to MongoDB's default port.

Metadata: Logged as a native JSON object.

Adding Custom Transports

Adding a custom transport (say for one of the datastore on the Roadmap) is actually pretty easy. All you need to do is accept a couple of options, set a name, implement a log() method, and add it to the set of transports exposed by winston.

What's Next?

Inspirations

Road Map

Graylog2 format support.

Improve support for adding custom Transports not defined in Winston core.

Create API for reading from logs across all transports.

Add more transports: Redis

Run Tests

All of the winston tests are written in vows, and cover all of the use cases described above. You will need to add valid credentials for the various transports included to test/test-config.json before running tests: